This invention relates generally to the field of optical telescopes and, more particularly, to an automatic alignment and tracking telescope apparatus and method for automatically aiming to and tracking any of a pre-determined plurality of celestial points.
Telescopes for viewing of celestial bodies employ various known arrangements of lenses and mirrors to gather light from a selected light source, typically a star, and project the gathered light onto an image plane with significant magnification. Under well-known principles of optics, however, the effective field of view across the image plane in inversely proportional to the magnification. Therefore, at high magnifications, the image plane may be very small. This poses a problem when the user of the telescope wishes to view a particular star because, due to the rotation of the earth, the star will appear to move across the image plane and be lost from sight within seconds of being at the center of the image plane. Such motion, if not compensated by a counter-motion of the telescope, is more than merely frustrating to the viewer, it would render taking a photograph of any star image impossible. Further, many star images are so faint that they are not visible to the naked eye and, therefore, can be seen only by a substantial time exposure of the faint light onto the film. If the telescope were unable in track with the rotation of the earth to maintain a fixed image point on the film, such time exposure would be impossible.
For this reason various alignment and tracking mechanisms have been known in the art. All, however, have shortcomings.
One known alignment and tracking mechanism is the Celestron(copyright) Compustar(copyright). The Compustar(copyright) has a single axis drive motor and operates as follows:
First the power is turned on and the on-board processor is initialized. The initialization causes the telescope tube to point to a center reference of the drive base. Next, the user manually aligns the telescope forks toward Polaris, otherwise known as the xe2x80x9cnorth starxe2x80x9d. The user then enters, through a keypad means, the Greenwich Mean Time (xe2x80x9cGMTxe2x80x9d) and the longitude and latitude of the telescope position. Since the telescope forks have been aligned toward the north star, the on-board processor has sufficient data to point the telescope to Polaris, which it does. Due to various factors, including mechanical clearances and backlash, approximation of the longitude and latitude, and initial pointing error of the telescope forks, the automatic pointing toward Polaris is not perfect. The user must therefore center Polaris in the finderscope and eyepiece. The centering allows the Compustar(copyright) telescope to more accurately track star images after the alignment procedure is completed.
After centering Polaris the user press a keypad button whereupon the on-board computer generates signals which cause the telescope drive motor to point the tube to a second alignment star. As with the operation of pointing the tube toward Polaris, however, the pointing to the second alignment star is not perfectly centered. The user therefore manually centers the second alignment star in the finderscope and eyepiece and enters a xe2x80x9ccompletexe2x80x9d command through the keypad. The Compustar can then track essentially any star image in the sky that the user selects.
The Celestron(copyright) Compustar(copyright) system and single axis drive, although a significant partial solution to the known problems of telescope mounting and tracking methods, lack features identified by the present inventors.
An object of the present invention is to provide a portable, economical, stable and easy to use apparatus for aligning, aiming and tracking a telescope on any celestial body selected by the user.
An embodiment of the invention comprises a tripod, quadrapod or similar structure for supporting a movable mount at a given height above ground, the movable mount having structure for securely attaching a telescope aligned with a pointing axis. The telescope has an eyepiece for viewing a focussed image collected by the telescope, and a finderscope for alignment purposes. The embodiment further includes at least two servo motors for moving the movable mount along two axes of movement. The embodiment also has a microprocessor for calculating and generating control signals for the servo motors, a program memory and a star data memory, a manual data entry key pad for inputting commands and data into the processor, and a display means.
A further embodiment includes a level-indicating device to detect the pointing axis of the tube being level with respect to ground, i.e., the plane tangential to earth at the location of the supporting structure. A still further included is a compass for indicating the azimuth angle of the tube pointing axis with respect to North.
Before operating the automatic alignment apparatus and method of the invention, the user first levels the telescope tube with respect to ground, using the level-indicator, and points the telescope tube north using the compass.
The user then enters the following data, through a keypad device connected to the apparatus""s controller: the date, the local time, and the longitude and latitude where the user and the telescope are located. The user then enters a start command, by pressing an xe2x80x9cENTERxe2x80x9d key or equivalent, via the manual data entry pad and, in response:
1. The processor retrieves a position data for a first bright star from pre-loaded star data memory;
2. The processor calculates the servo control signals for pointing the telescope to the first bright star, based on the retrieved position data, the local data and time, and the longitude and latitude entered by the user;
3. In response, the generated servo control signals the servos automatically point the telescope to the first bright star; and
4. The processor generates a audible or visual signal indicating to the user to center the star in the finderscope and eyepiece.
The user centers the first bright star in the eyepiece viewing field and presses an xe2x80x9cALIGNxe2x80x9d or equivalently named button. In response, the processor:
5. Retrieves a position data for a second bright alignment star from the pre-loaded star data in memory;
6. Calculates and generates the servo control signals for pointing the telescope to the first bright star, based on the retrieved position data, the local data and time, and the longitude and latitude entered by the user;
7. In response to the generated servo control signals, the servos automatically point the telescope to the second bright alignment star; and
8. The processor generates a audible or visual signal indicating to the user to center the second bright star in the finderscope and eyepiece.
The user then centers the first bright star in the eyepiece viewing field and presses a START button again. The processor then generates a audible or visual signal indicating to the user that the alignment is complete.
After the alignment is complete the user enters a star identification number for any of the large number of stars stored in the star data. In response, the controller generates servo control signals which operate the servos to align the telescope on the selected star and to track the star to compensate for the rotation of the earth.